1. Field of the Invention
The present invention relates to a power transfer device adapted for use in combination with a primary transmission for four-wheel drive vehicles.
2. Description of the Prior Art
Disclosed in Japanese Patent Laid-open Publication No. 63-269729 is a power transfer device adapted for use in combination with a power transmission, which comprises a housing adapted to be secured to one end of the power transmission casing, a first output shaft rotatably mounted within the housing for drive connection to a set of rear road wheels, a second output shaft rotatably mounted within the housing in parallel with the first output shaft for drive connection to a set of front road wheels, a center differential in the form of a planetary gear unit mounted on the first output shaft to transfer input drive torque to the first and second output shafts, a drive sprocket rotatably mounted on the first output shaft and drivingly connected to a driven sprocket mounted on the second output shaft, and a changeover mechanism mounted on the first output shaft to selectively transfer the drive torque from an output element of the planetary gear unit to the drive sprocket. In the power transfer device, the planetary gear unit includes a carrier having a tubular hub portion arranged in surrounding relationship with the first output shaft and associated with the changeover mechanism, and the drive sprocket is arranged between the planetary gear unit and the changeover mechanism and rotatably supported on the tubular hub portion of the carrier. In such an arrangement, it is required to supply lubricating oil into double spaces among the first output shaft, the tubular hub portion of the carrier and the drive sprocket, and it is also required to assemble a bearing respectively within the double spaces among the first output shaft, the tubular hub portion of the carrier and the drive sprocket. This results in a complicated mounting construction of the drive sprocket.